Integrated circuits and microsystems are fabricated from wafers, or substrates, of silicon or any other semiconductor material, which undergo a series of steps of deposition of thin films of various materials, masking and lithography of these films, then etching of these same films. Between these fabrication steps are inserted steps of cleaning of the equipment and also steps of inspection of product quality.
In chemical depositions, an adsorption, a chemisorption or a heterogeneous reaction happens at the surface of the substrate to be covered. In the case of a chemical vapor deposition, this reaction happens on all the substrates in which the conditions of temperature, pressure and concentration of the reagents are present. The result is that the chemical deposits uniformly cover the surface with patterns formed on the substrates, even those that are substantially vertical. This feature is particularly useful in the fabrication of recent circuits and microsystems wherein the patterns to be covered can have very high shape factors (ratio of the width to the height of the pattern).
CVD equipment generally comprises a processing chamber wherein are housed a substrate support and a gas distribution assembly, also known by the term “showerhead.” The latter delivers chemical agents in gaseous form, also known as “processing gas,” or “precursors,” close to the substrate. The support has an upper face suitable for holding the substrates and a lower face, opposite its upper face. The substrate support divides the inside of the processing chamber into an upper space and a lower space. The upper space is found on the side of the upper face of the support and is delimited by the walls of the processing chamber. The lower space is found on the side of the lower face of the support and is delimited by the walls of the processing chamber.
A purging gas is injected into the lower space of the processing chamber to limit contamination of the walls of the chamber by the chemical agents injected by the showerhead into the upper space of the chamber.
The Applicant has proposed the use of a gas discharge ring disposed around the support. The gas discharge ring allows a more homogeneous circulation of the gases flush with the substrates. This is, for example, described in the French patent application published under the number FR 2 930 561 and filed by the Applicant.
Accidental reactions between the gases or between a gas and a wall can occur and lead to solid deposits in the form of accidental films in unwanted places.
Accidental reactions can cause clogging of apertures of a gas discharge assembly and particularly the gas discharge ring. The clogging of some apertures disturbs the circulation of the gases and the quality of the products is affected thereby.
Moreover, the gas discharge assembly, once blocked, no longer fulfils its function adequately. Reactive gas flows are no longer homogeneous. The rest of the equipment, and particularly the reaction chamber, is in turn subject to accidental reactions at its surface. The particular contamination of the equipment impairs its effectiveness. The contamination makes it necessary to frequently clean the gas discharge assembly, the gas discharge ring and the rest of the chamber, which affects the availability of the processing chamber. Accidentally deposited films are liable to be transferred onto a substrate to be processed and thus affect the quality of thin film depositions. This is not satisfactory.
These accidental deposits are greater the higher the temperature. However, the support for the substrates is heated so that the substrates reach the temperature needed for the desired reactions. To limit phenomena of condensation of the reactive gases in contact with the distribution system, the latter is heated. The rest of the device thus tends to also be heated.
In so-called high-temperature conditions, typically between 600° C. and 800° C., these depositions require even more frequent cleaning and maintenance, which make the devices industrially unusable in these fields.